Prominin–1 Deficiency Leads to Progressive Retinal Degeneration

Abstract

Abstract: : Purpose:Prominin–1/CD133 (Prom–1) is a pentaspan membrane glycoprotein specifically associated with plasma membrane protrusions. A frameshift mutation in the human PROM–1 has been reported to cause a retinal degeneration. Given that Prom–1 is expressed in the rod photoreceptors the goal of our study is to delineate the role of this molecule during retinal development. Methods: Prom–1 knock out mice (Prom–1^–/–) were generated, and general retinal structures were observed by immunohistochemistry and electron microscopy. TUNEL assays were performed to detect abnormal cell death, and functional abnormalities of Prom–1^–/– animals were evaluated by an electroretinography (ERG). Results:Progressive retinal degeneration evidenced by photoreceptor loss was observed in Prom–1^–/– retinas; the total areas of the outer nuclear layer (ONL) was reduced to 59.5+/–4.4 % and 41.2+/–3.4 % compared to WT retinas at P20 and P90, respectively. In older animals, e.g. 13 months, the entire photoreceptor layer was disappeared. Increased apoptosis in the ONL was already evident at P15 in Prom–1^–/– retinas (5.3+/–0.5–fold increase in the number of TUNEL positive cells compared to WT retinas), and progressed drastically by P20. Immunohistochemical analyses of GFAP showed remarkable up–regulation in P20 Prom–1^–/– retinas. Rhodopsin staining and electron microscopy revealed a disorganization of the rod outer segments in younger Prom–1^–/– animals. However, microvilli and basal infoldings of pigmented epithelial cells were not affected in Prom–1^–/– animals. In agreement with a retinal degeneration, the ERG recorded at P30 shows reduced responses in Prom–1^–/– mice. Conclusions: In the retina, Prom–1 is a critical molecule for proper development and survival of rod photoreceptors.

Keywords: retinal degenerations: cell biology • photoreceptors